Seriously, how much is Facebook worth? It's been an enigma in tech gossip for years now, as the social-networking company grows bigger and bigger and yet remains privately held. And some of Facebook's most rapid growth has taken place in the midst of a stormy economic climate that could batter any company's balance sheet. So here's a rundown of what tech blogs, news outlets, investors, and Valley gadflies have said thus far about just how much Facebook is worth.

Are all these numbers accurate? In a word, no. Some of them were rumors (albeit decently strong ones, as we've omitted some of the more ridiculous ones), and others refer to Facebook's preferred-stock valuation, which as we learned during its legal tiff with onetime rival ConnectU, that isn't necessarily anywhere close to the company's paper valuation.

One thing that's interesting: Take a look at the trajectory. Facebook's perceived valuation keeps climbing and climbing and climbing right up to its $240 million investment by Microsoft. Then, once the hype dies down (and the market starts to sputter) it tanks. It's not until, perhaps not coincidentally, the departure of chief financial officer Gideon Yu and the stronger likelihood of a new investment round that Facebook's valuation starts to climb again.

What's next? Digital Sky Technologies' investment in Facebook assumed a preferred-stock valuation of $10 billion, and employee stock trades have started at about a $6.5 billion valuation. It's not yet clear how much more the company's worth will fluctuate before, at long last, founder and CEO Mark Zuckerberg and his team decide to take it public. That is, of course, assuming that actually happens.

Playing the Facebook valuation game
Everyone's constantly talking about how much Facebook is worth. But how much has that number changed over the past few years? A lot, it turns out. Here's our cheat sheet.

Few thousand

February 2004: Backed by a few thousand dollars from its co-founders,
Facebook goes live as a small, minimalist social-networking site limited
to Harvard undergraduates.

$10 million

June 2004: PayPal co-founder Peter Thiel becomes Facebook's first outside investor. He invests $500,000 into the 4-month-old social network, which has by now taken its home base of Harvard and a scattering of other elite colleges by storm. Later that year, there are shaky rumors that Friendster--still a major player in U.S. social networking at the time--offered $10 million for Facebook and was turned down.

$100 million

April 2005: Facebook raises a $12.7 million Series A round of funding from Accel Partners. Rumors peg its valuation at about $100 million.

$750 million

March 2006: BusinessWeek reports that Facebook turned down a $750 million acquisition offer and was shopping itself to potential buyers at closer to $2 billion.

$525 million

April 2006: Facebook raises its Series B round of funding to the tune of $25 million. The round is led by Greylock Partners, with contributions from Meritech Capital Partners, and prior investors Accel Partners and Peter Thiel. The company's pre-money valuation is reported to be$525 million.

December 2006: Early Facebook investor Peter Thiel, who fueled the small social network with $500,000 in June 2004, tells Bloomberg that he believes the company is worth as much as $8 billion but says it is not for sale.

$15 billion

October 2007: Microsoft invests $240 million in Facebook at a $15 billion valuation. Although it's not really made clear at the time, the company later clarifies that this investment was in preferred stock and that therefore $15 billion is not the company's actual valuation.

$3.75 billion

June 2008: Previously redacted court documents from ConnectU v. Facebook, the trial in which the creators of a onetime rival social network at Harvard sued Facebook CEO Mark Zuckerberg--claiming he stole their code and business plan--reveal that at this time, Facebook valued itself at $3.75 billion.

March 2009: Months later, the Silicon Valley rumor mill still won't stop talking about employees' private sales of Facebook stock--and apparently, the numbers aren't too pretty. The figures tossed around indicate that the stock is trading at a valuation well south of $3 billion. Later in March, Facebook CFO Gideon Yu leaves the company. Persistent rumors hint that he was unable to secure new funding for the company.

$2 billion

April 2009: TechCrunch reports that Facebook received a term sheet from potential investors with a valuation of $2 billion and turned it down.

$4 billion

April 2009: On the same day, VentureBeat reports that Facebook was on the verge of accepting new funding at a $4 billion valuation, but that Zuckerberg said no.

May 2009: Later in the month, Facebook finally gets that long-rumored cash. The company receives an investment of $200 million from the Russian firm Digital Sky Technologies at a $10 billion preferred-stock valuation. Also included: a plan to buy back a limited amount of vested employee stock.

$6.5 billion

July 2009: Digital Sky Technologies begins its buyback of up to $100 million in Facebook employee shares. Each share of common stock is selling for $14.77, which assumes a valuation of $6.5 billion for the company.